The earth's crust is subject to stresses that are the combined result of gravitational loading and heat-transfer-driven tectonic processes. One class of responses to these stresses can be described as brittle behavior responses. These responses include the formation and propagation of fractures, both extensional and shear. In geological terminology, shear fractures that accommodate measurable amounts of displacement are called faults.
Geologic slip tendency analysis is a technique that permits assessment of stress states and related potential fault activity. The tendency of a surface to undergo slip in a given stress field depends on its frictional characteristics (primarily controlled by rock type) and its “slip tendency”. The latter measure is defined as the ratio of shear stress to normal stress acting on a fault surface. Slip tendency analysis has been used successfully to characterize fault slip and fault slip direction in stress regimes associated with normal, reverse, and strike-slip faulting.
Related to slip tendency analysis, are “stress inversion” calculations, i.e., the determination (inversion) of the stress tensor from the effects of that stress tensor. Data sources for existing stress inversion methods have included earthquake focal mechanisms, paleostress indicators, and micro-seismicity. These methods rely on knowledge of the slip vector field generated by the stress state being sought.